[Elecraft] [K2] Odd AGC problem with K60XV installed

[Don Wilhelm]

Bill,

I am glad to hear it has not re-occurred.  I think your analysis is 
correct, except that it would be ALC and power control that would be 
affected, not AGC.

73,
Don W3FPR

On 12/16/2020 3:07 PM, Bill Coleman wrote:
> Don,
>
> Just a quick follow-up. I’m going to close the book on this problem, as it has not come up again, despite leaving the K2 on a couple of days.
>
> I think your diagnoses was spot on, I think a 15 MHz oscillation of the K60XV VRFDET components was causing the K2 to think the AGC was being activated under certain conditions.
>
> I think the oscillation might have been precipitated due to some waxy flux left between the pins of the LM368.
>
> Thank you for your assistance, as always.
>
>> On Dec 7, 2020, at 8:35 PM, Bill Coleman <aa4lr at arrl.net> wrote:
>>
>> I’m going to set it up in the damp basement at my other QTH. That’s where I saw the problem originally. Will let you know if it comes back.
>>
>>> On Dec 7, 2020, at 11:43 AM, Don Wilhelm <donwilh at embarqmail.com> wrote:
>>>
>>> Bill,
>>>
>>> It does sound like it is fixed.  Just be aware that some intermittents do find their way back, so knowing the symptoms you can recognize it quickly.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>> On 12/6/2020 6:30 PM, Bill Coleman wrote:
>>>> Don,
>>>>
>>>> I set the K2 up this weekend to try to reproduce this problem. Once again I opened it up and re-installed the K60XV board. I put a scope probe on P1 pin 6.
>>>>
>>>> I did not see the AGC failure mode right away, but I did find an intermittent oscillation on pin 6 at about 15 MHz. It would come and go, but no AGC activation.
>>>>
>>>> I removed the board and re-soldered all the components around the LM358. Then I inspected the board and scraped away any residual solder flux in that area of the board between any pins.
>>>>
>>>> I also re-soldered the 4.0 MHz resonator, although I did not hear or detect any relay activation when it failed before.
>>>>
>>>> After that, I put the board back in with the scope probe and ran it on the workbench for a day. I saw no AGC failure mode and no more 15 MHz oscillation.
>>>>
>>>> So, maybe it is fixed? Fingers crossed.
>>>>
>>>>
>> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
>> Web: http://boringhamradiopart.blogspot.com
>> Quote: "Not within a thousand years will man ever fly!"
>>             -- Wilbur Wright, 1901
>>
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> Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
> Web: http://boringhamradiopart.blogspot.com
> Quote: "Not within a thousand years will man ever fly!"
>              -- Wilbur Wright, 1901
>